The present invention relates to methods and components for making microelectronic assemblies.
Certain techniques for making semiconductor chip assemblies and similar microelectronic assemblies involve attaching leads to a microelectronic element and deforming the leads. One such process is disclosed in commonly assigned U.S. Pat. No. 5,518,964, the disclosure of which is hereby incorporated by reference herein. In certain embodiments described in the ""964 patent, a first element such as a dielectric layer in a connection component is provided with a plurality of elongated, flexible leads extending along a surface of the element. Each lead has a terminal end permanently attached to the first element and has a tip end offset from the terminal end. The tip ends of the leads may be releasably secured to the first element. The contacts of a second element such as a semiconductor chip are engaged with the first element or connection component, and the tip ends of the leads are bonded to contacts. The elements are then moved away from one another so as to deform the leads and provide vertically extensive leads extending between the first and second elements, i.e., between the chip and the connection component. A compliant material may be introduced between the chip and the connection component.
One method of moving the first element with respect to the second element in order to deform the leads is to provide opposed platens. Each platen engages one of the first element and the second element and moves the first element with respect to the second element. The platens are attached to conventional drive mechanisms for accomplishing the same. The platens may be moved a predetermined distance in one or more directions to deform the leads to a desired shape or to a desired vertical dimension.
Despite the foregoing improvements, further advancement in microelectronic assemblies is desirable.
The present invention addresses these needs.
In one aspect of the present invention, a method of making a microelectronic assembly comprises providing a first side assembly having a top surface and an oppositely facing bottom surface and a second side assembly having a first surface, the first surface being juxtaposed with the bottom surface. Leads are provided so that they extend between the first side assembly and the second side assembly and a first resilient element is disposed between the first side assembly and the second side assembly. A compressive force is applied to the juxtaposed assemblies so as to compress the first resilient element. The compressive force is at least partially released so that the first resilient element expands, thereby moving one or both of the first side assembly and second side assembly to deform the leads. After applying the compressive force, controlled movement of the elements of the assembly is no longer required. The resilient element is allowed to expand in order to deform the leads into the desired configuration.
The step of providing a first side assembly preferably includes providing a microelectronic element. The First resilient element may be attached to the first side assembly. The leads desirably extend between the microelectronic element and the second side assembly.
The leads preferably include a first end and a second end. In certain preferred embodiments, the first ends of the leads are preferably bonded to contacts on the microelectronic element and the second ends of the leads are attached to the second side assembly.
The first side assembly may comprise a frame having an aperture for receiving a microelectronic element, which may be inserted into the aperture.
The second side assembly may comprise a flexible dielectric layer.
The first resilient element preferably comprises a material having a low compression set and more preferably has a final height after removing the compressive force of 80% to 100% of the initial height before the compressive force is applied. The low compression set material may comprise, for example, a flexibilized epoxy. The first resilient element may be porous.
Providing the first side assembly may include providing an auxiliary element and providing the first resilient element between the auxiliary element and the second side assembly. The auxiliary element may be disposed in a number of positions with respect to the microelectronic element. In certain embodiments, the auxiliary element is disposed adjacent the microelectronic element and confronts the first side assembly, the second side assembly or both. The auxiliary element may have a central region extending over a surface of the microelectronic element and a peripheral region lying outwardly of the central region and the first resilient element includes at least one resilient pad disposed between the peripheral region and the second side assembly. The central region of the auxiliary element may be attached to the microelectronic element.
In certain embodiments, the auxiliary element comprises at least one post extending alongside the microelectronic element. The first resilient element is attached to the at least one post so that the resilient element extends between the at least one post and the second side assembly and attached to the microelectronic element.
The leads may be provided so that first ends of the leads are permanently attached to the second side assembly and second ends of the leads are releasably attached to the second side assembly. As the compressive force is at least partially released, the second ends of the leads are preferably peeled from the second side assembly.
In certain preferred embodiments, the first resilient element may be provided by stencil printing a composition onto at least one of the first side assembly and the second side assembly. The composition may be a curable composition and the curable composition may be cured to form the first resilient element.
The method desirably includes providing a structure and juxtaposing the structure over the microelectronic element. The structure may comprise a heat spreader and a second resilient element is desirably applied to a surface of the structure facing the microelectronic element. Adhesive may be applied to a surface of the structure which faces the microelectronic element. The adhesive may be curable and the method may include curing the adhesive while applying the compressive force. The structure may be attached to the first side assembly. Alternatively, the method may include juxtaposing a coverlay over the structure and attaching the coverlay to the first side assembly.
The deformed leads are preferably encapsulated by disposing a curable composition around the leads and curing the composition. The cured composition is preferably compliant.
In certain preferred embodiments, the first side assembly includes a plurality of microelectronic elements. The second side assembly comprises a dielectric layer and the method may further comprise cutting through the dielectric layer around the microelectronic elements. The first side assembly may comprise a wafer having a plurality of microelectronic elements.
The compressive force may be applied by applying an elevated pressure to a surface of the first side assembly that faces away from the second side assembly. In the alternative, a vacuum is applied to a surface of the first side assembly that faces the second side assembly.
The leads may be comprised of any conductive material, such as, for example, copper, gold, gold alloys and copper allows.
Other conductive elements may be included in the assembly. Solder balls may be attached to the second side assembly, preferably so that they are connected to the leads. The first side assembly may include a conductive plane disposed on a bottom surface thereof.
Another aspect of the invention is a microelectronic package made by providing a first side assembly having a top surface and an oppositely facing bottom surface and a second side assembly having a first surface, the first surface being juxtaposed with the bottom surface. Leads are provided so that they extend between the first side assembly and the second side assembly and a first resilient element is disposed between the first side assembly and the second side assembly. A compressive force is applied to the juxtaposed assemblies so as to compress the first resilient element. The compressive force is at least partially released so that the first resilient element expands, thereby moving one or both of the first side assembly and second side assembly to deform the leads.